Frequency domain reflectometer and method of compensating for transmission line attenuation

ABSTRACT

Frequency domain reflectometer and method of determining severity of faults in a transmission line are disclosed. The reflectometer compensates for attenuation effects in the transmission line when determining severity of faults. In general, the reflectometer applies a sweep signal to the transmission line in order to obtain a reflected sweep response signal. Then, the reflectometer obtains a sweep response spectrum from the reflected sweep response signal. The reflected sweep response signal includes a plurality of spectral peaks which represent the frequency components of the reflected sweep response signal. Then, the reflectometer determines a first attenuation compensation factor for a first spectral peak of the reflected sweep response spectrum. Furthermore, the reflectometer adjusts the reflected sweep response spectrum for effects due to attenuation in the transmission line by applying the attenuation compensation factor to the first spectral peak, thus compensating the reflected sweep response spectrum for attenuation within the transmission line. The reflectometer then obtains from the adjusted sweep response spectrum severity of an impedance mismatch in the transmission line.

FIELD OF THE INVENTION

The present invention relates generally to compensating for attenuationeffects of a transmission line, and more particularly, to a frequencydomain reflectometer that compensates for attenuation effects indetermining severity of impedance mismatches in a transmission line.

BACKGROUND OF THE INVENTION

Community Antenna Television ("CATV") systems are used in a widespreadmanner for the transmission and distribution of television signals toend users, or subscribers. In general, CATV systems comprise atransmission subsystem and a distribution subsystem. The transmissionsubsystem obtains television signals associated with a plurality of CATVchannels and generates a broadband CATV signal therefrom. Thedistribution subsystem then delivers the CATV broadband signal totelevision receivers located within the residences and businessestablishments of subscribers. The complexity and size of thedistribution subsystem requires that operation and performance beperiodically tested and/or monitored.

One test often performed by CATV service providers in order to pinpointproblems in the distribution subsystem is fault detection. Faultdetection refers to the process of locating faults within thedistribution subsystem such as breaks, shorts, discontinuities, degradedcomponents, and improperly terminated transmission lines. Faults withinthe distribution subsystem are typically characterized by an impedancemismatch. In other words, the impedance of the fault is typicallydifferent than the characteristic impedance of the transmission lines ofthe distribution subsystem. For example, transmission lines in a CATVdistribution subsystem typically have an impedance of approximately 75ohms; however, a short on the transmission line would have anapproximately zero impedance and a break would have an approximatelyinfinite impedance.

One problem with faults in the distribution subsystem is that faults,due to their impedance mismatch characteristics, reflect signalstransmitted through the distribution subsystem. As a result, beyondcutting off portions of the distribution subsystem in the case of ashort or a break, faults in the distribution subsystem may also causeproblems throughout the distribution subsystem due to interference fromreflected signals. Therefore, it is important for CATV service providersto be able to locate faults within the network in order to repair thefault to not only cure reception problems of a single subscriber but toremove fault generated interference from the distribution subsystem as awhole. While impedance mismatches within the distribution subsystem mayinterfere with CATV signals, some impedance mismatches due to theirseverity may not generate enough interference to justify the cost ofrepair. As a result, CATV service provides also need informationconcerning the severity of the impedance mismatch.

One way of determining location and severity of faults within thedistribution subsystem is to perform frequency domain reflectometry uponthe distribution subsystem. Frequency domain reflectometry utilizes areflectometer that applies a sweep signal to the distribution subsystem.The sweep signal is an RF signal that is swept from a start frequency toa stop frequency. If an impedance mismatch exists within thedistribution subsystem, the impedance mismatch will reflect eachtransmitted signal back to the reflectometer at the same frequency asthe transmitted signal but retarded in phase. As a result of thisreflection, a standing wave is generated. The reflectometer measures thelevel of the standing wave at each swept frequency in order to obtain areflected sweep response signal. The retardation of the reflected sweepresponse signal is such that the minimums of the reflected wave willalign to 1/2 the wavelength of the impedance mismatch from thereflectometer. Due to this known relationship, the reflectometer maydetermine the distance from the reflectometer of the impedance mismatch.

To this end, the reflectometer may perform spectral analysis upon thereflected sweep response signal in order to obtain a reflected sweepresponse spectrum having a plurality of spectral peaks. Each spectralpeak includes a frequency and a magnitude that together represent asinusoidal component of the reflected sweep response spectrum. Thereflectometer may apply the above wavelength relationship to thefrequency of a spectral peak in order to determine distance from thereflectometer of an impedance mismatch within the transmission line.Furthermore, the reflectometer may determine severity of the impedancemismatch from the magnitude of the spectral peak.

One problem associated with the above reflectometry system is thefailure to account for loss due to attenuation within the transmissionline. Transmission lines generally dampen the magnitude of sinusoidalsignals that are traveling through the transmission line as a functionof distance and as a function of the square root of the frequency. As aresult of this dampening, the magnitude of the spectral peak shouldactually be greater in magnitude in order to accurately represent theseverity of the impedance mismatch. Therefore, if the reflectometerfails to account for this loss due to attenuation, the reflectometer mayindicate that an impedance mismatch is not severe enough to requirerepair even though the impedance mismatch actually is severe enough.

Accordingly, there is a need for a reflectometer that accounts forattenuation effects when determining severity of impedance mismatcheswithin a transmission line. However, the effect of attenuation on themagnitude of a spectral peak has no closed form. As a result,determination of an appropriate attenuation compensation factor for aspectral peak may be computationally intensive. In order to support acomputationally intensive function, a reflectometer may need advancedprocessing circuitry thus adding to the cost of the reflectometer.Accordingly, there is also a need for a reflectometer that determines anappropriate attenuation compensation factor in a non-computationallyintensive manner.

SUMMARY OF THE INVENTION

The present invention fulfills the above need, as well as others, byproviding a frequency domain reflectometer that compensates forattenuation effects within the system under test when determine severityof a fault. In general, the reflectometer obtains a reflected sweepresponse spectrum that includes a plurality of spectral peaks whichrepresent the frequency components of the reflected sweep responsesignal. Then, the reflectometer adjusts magnitudes of the spectral peaksfor effects due to attenuation in the system under test. Thereflectometer adjusts the magnitudes by applying a separate attenuationcompensation factor to each spectral peak of the reflected sweepresponse spectrum. The reflectometer may obtain the attenuationcompensation factor in a variety of ways. For example, the reflectometermay (i) calculate the attenuation compensation factor for each spectralpeak, (ii) calculate at least one attenuation compensation factor andinterpolate the remaining attenuation compensation factors from thecalculated attenuation compensation factor, and (iii) obtain at leastone attenuation compensation factor from a table of attenuationcompensation factors and interpolate the remaining attenuationcompensation factors from the obtained attenuation compensation factor.

An exemplary method according to the present invention is a method ofdetermining severity of impedance mismatches in a system under test. Onestep of the method includes the step of applying a test sweep signal tothe system under test in order to obtain a reflected sweep responsesignal from the system under test. The reflected sweep response signalrepresentative of a frequency response of the system under test. Anotherstep of the method includes the step of generating from the reflectedsweep response signal a reflected sweep response spectrum that includesa plurality of spectral peaks. The method also includes the step ofdetermining a first attenuation compensation factor for a first spectralpeak of the plurality of spectral peaks. Furthermore, the methodincludes the step of adjusting the reflected sweep response spectrum foreffects due to attenuation in the system under test in order to obtainan adjusted sweep response spectrum by applying the attenuationcompensation factor to a first magnitude of the first spectral peak.Finally, the method also includes the step of obtaining from theadjusted sweep response spectrum a severity of an impedance mismatch inthe system under test.

The present invention further includes various apparatus for carryingout the above method. For example, one apparatus according to thepresent invention includes a connector, a transmitter circuit, ameasurement circuit, an analog-to-digital (A/D) converter, and a digitalsignal processing (DSP) circuit. The connector is configured to couplethe system under test to the apparatus. The transmitter circuit iscoupled to the connector and is configured to apply a test sweep signalto the connector and the system under test coupled thereto. Thereflected sweep response signal representative of a frequency responseof the system under test. The measurement circuit is coupled to theconnector and is configured to generate a plurality of measurementsignals indicative of a resultant response signal. The resultantresponse signal includes (i) the test sweep signal from the transmittercircuit and (ii) the reflected sweep response signal received from thesystem under test coupled to the connector. The A/D converter is coupledto the measurement circuit and is configured to generate from theplurality of measurement signals a digitized resultant response signalthat is a digital representation of the resultant response signal.

The DSP circuit is coupled to the A/D converter and is configured to (i)obtain the reflected sweep response signal from the digitized resultantresponse signal, (ii) generate from the reflected sweep response signala reflected sweep response spectrum that includes a plurality ofspectral peaks, and (iii) determine a first attenuation compensationfactor for a first spectral peak of the plurality of spectral peaks. TheDSP circuit is also further configured to (i) adjust the reflected sweepresponse spectrum for effects due to attenuation in the system undertest in order to obtain an adjusted sweep response spectrum by applyingthe attenuation compensation factor to a first magnitude of the firstspectral peak, and (ii) obtain from the adjusted sweep response spectruma severity of an impedance mismatch in the system under test. The firstspectral peak corresponds to a first distance traveled through thesystem under test. Furthermore, the first attenuation compensationfactor accounts for attenuation of a plurality of signals at differentfrequencies traveling the first distance through said system under test.

The above features and advantages, as well as others, will become morereadily apparent to those of ordinary skill in the art by reference tothe following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a frequency domain reflectometer that incorporates variousfeatures of the present invention;

FIG. 2 shows the reflectometer of FIG. 1 coupled to a subscriber networkunder test;

FIG. 3 shows in further detail the reflectometer of FIG. 1;

FIG. 4A shows a flowchart depicting a reflectometry procedure utilizedby the reflectometer of FIG. 1;

FIG. 4B shows a flowchart of an attenuation compensation procedureutilized by the reflectometer of FIG. 1;

FIG. 4C shows a flowchart of a harmonic suppression procedure utilizedby the reflectometer of FIG. 1;

FIG. 5 shows an exemplary reference sweep response signal;

FIG. 6 shows an exemplary resultant sweep response signal;

FIG. 7 shows an exemplary reflected sweep response signal;

FIG. 8 shows a simplified exemplary reflected sweep response spectrum;

FIG. 9 shows a portion of the reflected sweep response spectrum of FIG.8 in greater detail; and

FIG. 10 shows a spectrum for an attenuation factor equation.

DETAILED DESCRIPTION

FIG. 1 shows a simplified diagram of a frequency domain reflectometer("reflectometer") 10 that incorporates various features of the presentinvention therein. The reflectometer 10 includes a RF connector 12, acoupling device 13, a radio frequency ("RF") transmitter 14, ameasurement circuit 16, a reference impedance 17, an analog-to-digital("A/D") converter 18, a digital signal processing and controller circuit("DSP/controller") 20, a memory 21, a keypad 25, and a display 26. TheRF connector 12 is operable to couple the reflectometer 10 to atransmission line 24 under test, such as a coaxial cable of a subscribernetwork.

The RF transmitter 14 is connected to the RF connector 12 via thecoupling device 13. The RF transmitter 14 is an RF circuit operable togenerate RF signals including a sweep signal, wherein the sweep signalis an RF test signal in which the frequency of the RF test signal isswept over time over a predetermined frequency range. The RF transmitter14 is furthermore operable to generate the sweep signal in accordancewith a sweep control signal received from the DSP/controller 20. Inparticular, the RF transmitter 14 is operable to generate a sweep signalthat includes a first segment at a start frequency Fstart, a secondsegment at the start frequency Fstart plus a frequency increment freq₋₋inc (Fstart+freq₋₋ inc), a third segment at the start frequency Fstartplus two times the frequency increment freq₋₋ inc (Fstart+2*freq₋₋ inc),on so on, and including a last segment at a stop frequency Fstop. Forexample, the RF transmitter 14 in response to control signals receivedfrom the DSP/controller 20 may generate a sweep signal that includes afirst segment at 5 MHz, then a second segment at 5.075 MHz, then a thirdsegment at 5.015 MHz, and so forth, and including a last segment at 81.8MHz.

The measurement circuit 16 is also coupled to the RF connector 12 viathe coupling device 13. The measurement circuit 16 is a circuit operableto receive a resultant sweep signal comprising the incident sweep signaltransmitted by the RF transmitter 14 and the reflected sweep signalreflected by either the reference impedance 17 or impedance mismatchesin the transmission line 24. Furthermore, the measurement circuit 16 isoperable to generate measurement signals that are representative ofmagnitude of the resultant sweep signal received at each segment of thesweep signal.

The reference impedance 17 includes at least one resistor or otherimpedance device that provides an impedance equal to the desiredimpedance of the transmission line 24 under test. In the exemplaryembodiment, however, the reference impedance 17 includes a firstimpedance device 17a and a second impedance device 17b that each have animpedance level of 75 ohms which is the desired impedance of a CATVsubscriber network. By including two impedance devices, thereflectometer 10 is able to maintain proper termination of thetransmission line 24 under test while the reflectometer 10 internallydisconnects the transmission line 24 from the RF transmitter 14 during areference sweep. In particular, during a reference sweep the firstimpedance device 17a terminates the reflectometer 10 while the secondimpedance device 17b provides proper termination for the transmissionline 24 under test.

The coupling device 13 may suitably be any device or circuitry thatselectively connects the RF transmitter 14 to either the RF connector 12or the first impedance device 17a. Furthermore, the coupling device 13may also selectively couple the RF connector 12 to a second impedance17b when the RF transmitter 14 is not connected to the RF connector 12.The coupling device 13 may, for example, be a relay, diode switches,GaAs FET switches, or hybrid directional RF couplers. The couplingdevice 13 preferably includes a control input for receiving controlsignals that cause the coupling device 13 to connect a either the RFconnector 12 or the first impedance device 17a to the RF transmitter 14and the measurement circuit 16.

The A/D converter 18 is coupled to the measurement circuit 16. The A/Dconverter 18 is a circuit that is operable to produce a digitalrepresentation of the measurement signal received from the measurementcircuit 16. In particular, the A/D converter 18 generates an 8-bit valuethat is indicative of the DC level supplied by the measurement circuit16.

The DSP/controller 20 is coupled to the A/D converter 18 and the memory21. The DSP/controller 20 is operable to receive the digitized resultantsignal and to determine location and severity of impedance mismatches inthe transmission line 24. To this end, the DSP/controller 20 is operableto obtain the reflected sweep response signal from the digitizedresultant signal and to obtain a plurality of spectral peaks from thereflected sweep response signal by performing spectral analysis upon thereflected sweep response signal. The DSP/controller 20 is furtheroperable to adjust the spectral peaks for loss due to attenuation in thetransmission line 24 and to suppress harmonics in the reflected sweepresponse signal.

The DSP/controller 20 is also operably connected to control theoperations of the coupling device 13 and the RF transmitter 14. TheDSP/controller 20 may suitably be implemented with a microprocessor, adigital signal processing circuit, analog components, digitalcomponents, or any combination thereof. The DSP/controller 20 is furtherconnected to the keypad 25 and the display 26. The keypad 25 provides ameans for accepting user input and the display 26 provides a means forcommunicating results to a user. Results may alternatively becommunicated by an audible signal, including those generated usingspeech synthesis. Alternatively, results may be provided to acommunication port, not shown, to facilitate the transfer of the resultsinformation to a remote device.

In particular, the DSP/controller 20 is operable to provide the RFtransmitter 14 with sweep control signals that configure the RFtransmitter 14 to generate a sweep signal having a certain frequencyspan freq₋₋ span and a certain sweep resolution swp₋₋ res. For example,the DSP/controller 20 may provide the RF transmitter 14 with sweepcontrol signals which cause the RF transmitter 14 to sweep a RF testsignal from 5 MHz to 81.8 MHz at a sweep resolution swp₋₋ res of 1024sweep segments. In response to such control signals, the RF transmitter14 would generate a sweep signal that first transmits a test signal at 5MHz, then transmits a test signal at 5.075 MHz, then transmits a testsignal at 5.150 MHz, and so forth, and including a last segment at 81.8MHz.

The memory 21 is a circuit operable to store digital information. Thememory 21 primarily stores algorithms and routines executed by theDSP/controller 20. Furthermore, the memory 21 stores data generated andmanipulated by the DSP/controller 20.

FIG. 2 shows the frequency domain reflectometer ("reflectometer") 10 ofFIG. 1 connected to a system under test. The exemplary system under testis a subscriber network, in other words, a network associated with aCATV subscriber's residence, that includes a cable drop 40, a primarycable 42, a splitter 44, a first terminal cable 46, a second terminalcable 48, and a third terminal cable 50. It shall be noted that thesubscriber network of FIG. 2 is given by way of example only. Thereflectometer 10 of the present invention may readily be used insubscriber networks of any configuration, as well as non-subscriber CATVnetworks.

The primary cable 42, which may suitably be coaxial cable, connects thedrop 40 to the splitter 44. The splitter 44 is connected to provide RFsignals received from the primary cable to each of the first terminalcable 46, the second terminal cable 48, and the third terminal cable 50.The first terminal cable 46, the second terminal cable 48 and the thirdterminal cable 50 are further connected to one of a plurality ofterminal apparatus 56. The terminal apparatus 56 may include one or moretelevision receivers, a personal computing system, or any other devicereceiving or transmitting information through the subscriber network.The drop 40 connects the primary cable to a tap 58 into the CATVdistribution network, not shown.

In normal operation of the subscriber network, CATV signals generated bythe CATV service provider propagate from the tap 58 to the drop 40. TheCATV signals then propagate through the primary cable 42 to the splitter44. The splitter 44 provides the CATV signals to each of the firstterminal cable 46, the second terminal cable 48 and the third terminalcable 50. The first terminal cable 46, the second terminal cable 48, andthe third terminal cable 50 provide the CATV signals to the terminaldevices 56.

To test the subscriber network, the reflectometer 10 is connected to oneend of the subscriber network. Specifically, the reflectometer 10 isconnected via the RF connector 12 to the tap 58. It will be noted thatfor subsequent tests, the reflectometer 10 may be connected to eitherthe first, second, or third terminal cables 46, 48, and 50, respectivelyin an attempt to pinpoint impedance mismatches within the subscribernetwork.

The reflectometer 10 then performs a reference sweep. To this end, theDSP/controller 20 sends a control signal to the coupling device 13 thatcauses the coupling device 13 to couple the first impedance device 17ato the RF transmitter 14 and to couple the second impedance device 17bto the RF connector 12. The reflectometer 10 then transmits a sweepsignal such as that described above in connection with FIG. 1 which isapplied to the first reference impedance 17a.

The reflectometer 10 then generates a plurality of reference measurementsignals, each of which corresponds to one of the swept frequencies. Tothis end, the reflectometer 10 operates in the manner discussed above inconnection with the measurement circuit 16 of FIG. 1. The referencemeasurement signals are representative of the strength of a referencesweep signal at each swept frequency. The reflectometer 10 stores eachof the reference measurement signals in order to provide thereflectometer 10 with a reference sweep response signal during a testsweep.

After the reference sweep, the reflectometer 10 performs a test sweep.To this end, the reflectometer 10 transmits a test sweep signal that issubstantially the same as the reference sweep signal. The test sweepsignal propagates from the tap 58 to the drop 40. The test sweep signalthen propagates through the primary cable 42 to the splitter 44. Thesplitter 44 provides the test sweep signal to each of the first terminalcable 46, the second terminal cable 48 and the third terminal cable 50.The first terminal cable 46, the second terminal cable 48, and the thirdterminal cable 50 provide the sweep signal to the terminal devices 56.If there are impedance mismatches in the subscriber network, then eachimpedance mismatch that receives the test sweep signal will cause aportion of the test sweep signal to be reflected back to thereflectometer 10.

The reflectometer 10 then generates a plurality of measurement signals,each of which corresponds to one of the swept frequencies of the testsweep signal. To this end, the reflectometer 10 operates in the mannerdiscussed above in connection with the measurement circuit 16 of FIG. 1.The measurement signals are representative of the strength of aresultant sweep signal at each swept frequency. As stated above, theresultant sweep signal includes the test sweep signal generated by thereflectometer 10 plus any test sweep signals reflected by impedancemismatches within the subscriber network. The reflectometer 10 thenobtains the reflected sweep response signal by comparing the measurementsignals of the resultant sweep signal to the corresponding referencemeasurement signals generated during the reference sweep. The comparisonof the measurement signals with the reference measurement signals yieldsa reflected sweep response signal of the subscriber network. Thereflected sweep response signal comprises a level measurement for eachsegment of the sweep signal that is representative of the relationshipbetween the measurement signals of the reference sweep signal and themeasurement signals of the resultant sweep response signal.

If impedance mismatches resulting for example from damaged, poorquality, or improperly connected equipment is employed in the subscribernetwork, then the reflected sweep response signal will exhibit standingwave characteristics. To obtain location and severity of the impedancemismatches, the reflectometer 10 performs spectral analysis upon thereflected sweep response signal to obtain a plurality of spectral peakswhich represent the frequency components of the reflected sweep responsesignal. Each of the spectral peaks includes a magnitude indicative ofseverity of a possible impedance mismatch within the subscriber networkand a frequency indicative of location of the possible impedancemismatch within the subscriber network. The reflectometer 10 thenadjusts the magnitudes of the spectral peaks for loss due to attenuationeffects of the subscriber network. The reflectometer 10 then applies thefollowing distance equation D to the spectral peaks in order to obtaindistance to fault information: ##EQU1## where D is the distance in feetfrom the reflectometer 10 to a possible impedance mismatch within thesubscriber network, f_(R) is the frequency of a spectral peak obtainedfrom the reflected sweep response signal, c is the speed of light infeet per a microsecond, and Vop is the velocity of propagation throughthe transmission lines of the subscriber network. Once the reflectometer10 obtains the distance information, the reflectometer 10 suppressesspectral peaks that are harmonics of other spectral peaks. Finally, thereflectometer 10 displays location and severity information for each ofthe adjusted spectral peaks.

It should be noted that if the reflectometer 10 failed to adjust forattenuation effects, the reflectometer 10 may fail to indicate the trueseverity of an impedance mismatch which may result in a user determiningnot to repair an impedance mismatch that is actually severe enough toimpair the performance of the subscriber network. Furthermore, if thereflectometer 10 failed to suppress spectral peaks that are harmonics ofother spectral peaks, then the reflectometer 10 may falsely indicate animpedance mismatch within the subscriber network which in reality doesnot exist. As a result, the reflectometer 10 of the present invention,by providing attenuation compensation and harmonic suppression increasesthe accuracy of the information generated by reflectometer 10.

FIG. 3 shows in further detail a reflectometer 10 according to thepresent invention. For convenience, equivalent components in FIG. 1 areidentified by the same reference numerals in FIG. 3. In general, thereflectometer 10 includes a RF connector 12, a coupling device 13, a RFtransmitter 14, a measurement circuit 16, a reference impedance 17, anA/D converter 18, a DSP/controller 20, a memory 21, a keypad 25, and adisplay 26. The RF transmitter 14 includes a first oscillator circuit312, a second oscillator circuit 314, a mixer 316, a variable attenuator318, an output amplifier 320, a feedback detector 322, and anintegrating amplifier 326.

The first oscillator circuit 312 is a tunable oscillator circuitoperable to provide RF signals over a range of frequencies, for example,from 1655 MHz to 2450 MHz. Specifically, the first oscillator circuit312 has a control frequency input 328 connected to the DSP/controller 20for receiving sweep control signals therefrom. The first oscillatorcircuit 312 generates output RF signals having a frequency thatcorresponds to control signals received at the control frequency input328. To this end, the first oscillator circuit 312 also includes avoltage controlled oscillator ("VCO") and a VCO control circuitconfigured in a well-known manner to produce controlled RF signals.

The second oscillator circuit 314 is an oscillator circuit operable toproduce an RF signal having a fixed reference frequency. In theembodiment described herein, the second oscillator circuit 314 producesa reference frequency of 1650 MHz. The second oscillator circuit 314 maysuitably have the same structure as the first oscillator circuit 312.

The mixer 316 is operably coupled to receive RF signals from the firstoscillator circuit 312 and the second oscillator circuit 314 and togenerate a mixed RF signal therefrom. The mixed RF signal, or outputsignal, may be a segment of a sweep signal. In the exemplary embodimentdescribed herein, the mixer 316 is coupled to the second oscillatorcircuit 314 through first and second reference signal attenuators 330and 332, respectively, and a low pass filter 334. The mixer 316 iscoupled to provide the output signal to variable attenuator 318 througha first output signal attenuator 336, a one gigahertz low pass filter338, and a +22 dB amplifier 340.

The variable attenuator 318 is operable to attenuate the output signalin order to provide a level-adjusted output signal to the outputamplifier 320. The output amplifier 320 is preferably a +25 dBamplifier, and is further connected to provide an amplified outputsignal to the RF test connector 310 and the feedback detector 322. Thefeedback detector 322 is operable to receive the amplified output signaland generate a feedback signal having a DC level indicative of theamplified output signal magnitude. The feedback detector 322 is coupledto provide the feedback signal to the control loop amplifier 326. Thecontrol loop amplifier 326 is further coupled to the DSP/controller 20to receive a reference signal RF₋₋ ON from the DSP/controller 20. Thecontrol loop amplifier 326 is operable to provide an error signal to thecontrol input of the variable attenuator 318, wherein the error signalis based on the difference between the DC level of the reference signalRF₋₋ ON and the feedback signal.

The resister network 350 couples the RF circuit 14 to the couplingdevice 13 and the measurement circuit 16. The resistor network 350includes three resistors each having substantially the same impedance.The resistor network 350 helps isolate the sweep signal transmitted bythe RF transmitter 14 from the reflected sweep signal received fromeither the reference impedance 17 or the subscriber network connected tothe RF connector 12. This isolation is necessary in order for the abovedescribed feedback loop of the RF transmitter 14 to properly cause theRF transmitter 14 to generate a sweep signal that has a substantiallyconstant magnitude.

The measurement circuit 16 is operable to provide the A/D converter witha DC level that is indicative of the magnitude of the resultant sweepsignal which includes the sweep signal generated by the RF transmitter14 and the reflected sweep signal reflected by the reference impedance17 or the subscriber network under test. The measurement circuit 16includes a broadband detector 352, a capacitor 354, and an amplifier356. The broadband detector 352 is operable to receive the resultantsweep signal that includes the transmitted and reflected sweep signaland generate a measurement signal having a DC level indicative of theamplified resultant sweep signal. The capacitor 354 then filters themeasurement signal to remove any flutter, drift, or other AC componentsthat may be in the measurement signal. The amplifier 356 then receivesthe filtered measurement signal and amplifies the measurement signal inorder to provide a DC measurement signal having a suitable level for theA/D converter 18.

The A/D converter 18 then digitizes the received measurement signal. Inparticular, the A/D converter 18 generates an 8-bit value that isindicative of the DC level of the measurement signal and provides thisgenerated 8-bit value to the DSP/controller 20 for processing.

The DSP/controller 20 is operable to receive digital values from the A/Dconverter 18, control the operations of the RF transmitter 14, andperform the digital signal processing functions as described herebelowwith reference to FIGS. 4A, 4B, and 4C. In an exemplary embodiment, theDSP/controller 20 is implemented with a first microprocessor and a DSPengine. The first microprocessor is contained in a transmitter devicethat includes the coupling device 13, the RF transmitter 14, themeasurement circuit 16, and the reference impedance 17. Whereas, the DSPengine is contained in a receiver device that includes the keypad 25 andthe display 26. Furthermore, the DSP engine of the receiver deviceincludes a second microprocessor, a field programmable gate array("FPGA"), and memory. The first microprocessor of the transmitter devicecommunicates with the DSP engine of the receiver device via acommunication port and a cable not shown.

The above splitting of the reflectometer 10 into two devices fulfilled adesire for a package that may perform several types of tests upon asubscriber network. However if reflectometry measurements are the soleconcern of a transmission line analyzer, then it would be preferable toimplement the reflectometer in a single device having perhaps a singleprocessor for implementing the DSP/controller 20. In any event, theDSP/controller 20 may suitably be implemented with a microprocessor, adigital signal processing circuit, analog components, digitalcomponents, or any combination thereof. Furthermore, those of ordinaryskill in the art may devise other suitable DSP/controller circuitry.

In the embodiment described herein, a sweep plan is defined by a startfrequency Fstart, a stop frequency Fstop, and a sweep resolution swp₋₋res. The start frequency Fstart and the stop frequency Fstop define thelower and upper frequency limits of the sweep, while the sweepresolution swp₋₋ res defines the number of frequency points swept orsegments generated between the start frequency Fstart and the stopfrequency Fstop. For example, if the start frequency Fstart is equal to5 MHz, the stop frequency Fstop is equal to 81.8 MHz, and the sweepresolution swp₋₋ res is equal to 1024, then the sweep plan is intendedto take measurements at 5.000 MHz, 5.075 MHz, 5.150 MHz, 5.225 MHz, andso forth, and including 81.8 MHz. In the exemplary embodiment, the userdefines the sweep resolution swp₋₋ res by selecting via the keypad 25 apredefined sweep resolution. Alternatively, the user may define thesweep resolution swp₋₋ res by directly inputting values via the keypad25 of the reflectometer 10.

In any event, once the reflectometer 10 has the sweep plan, theDSP/controller 20 then provides a sweep control signal that correspondsto the sweep plan to the frequency control input 328 of the firstoscillator circuit 312. The sweep control signal is a signal that causesthe first oscillator circuit 312 to produce an RF signal having a sweptfrequency within some predefined range between 1655 MHz and 2450 MHz. Inparticular, the sweep control signal causes the first oscillator circuit312 to generate an RF signal between the stop frequency Fstop+1650 MHzand the start frequency Fstart+1650 MHz with a frequency incrementfreq₋₋ inc defined by the following equation: ##EQU2##

The swept RF signal is then provided to the mixer 316. The secondoscillator circuit 314, meanwhile, generates a fixed reference frequencyRF signal having a frequency of 1650 MHz. The fixed reference frequencysignal is also provided to the mixer 316 through the attenuators 330 and332 and the low pass filter 334.

The mixer 316 receives the RF signals from each of the first and secondoscillator circuits 312 and 314, respectively, and generates a sweepoutput signal therefrom. The sweep output signal is an RF signal havinga frequency that is swept in accordance with the sweep plan, in otherwords, from the start frequency Fstart to the stop frequency Fstop inincrements of freq₋₋ inc. The sweep output signal is then provided tothe variable attenuator 318. The variable attenuator 318 providesattenuation to the sweep signal at a level that corresponds to the DCvoltage appearing at its control input.

The DC voltage appearing at the control input of the variable attenuator318 provides level control to the output sweep signal. In any event, thevariable attenuator provides the level-adjusted sweep output signal tooutput amplifier 320. The amplifier 320 provides +25 dB of amplificationto the sweep signal to produce a relatively high power sweep outputsignal. The high power sweep output signal propagates to the RF output310, and is furthermore detected by the feedback detector 322.

The feedback detector 322 and the control loop amplifier 326 operate asa feedback path used to provide a high degree of control over the levelof the sweep output signal. To this end, the feedback detector 322generates a feedback signal having a DC level proportional to theamplitude or power of the sweep output signal. The control loopamplifier 326 receives the feedback signal from the feedback detector322, and furthermore receives a reference signal RF₋₋ ON from theDSP/controller 20. The control loop amplifier 326 compares the feedbacksignal to the reference signal RF₋₋ ON and generates an error signaltherefrom. The control loop amplifier 326 provides the error signal tothe control input of the variable attenuator 318. The error signalconstitutes a measure of the drift of the magnitude of the sweep outputsignal from the desired output level.

In particular, the desired output level in the embodiment describedherein is 30 dB. The magnitude of the sweep output signal tends to driftdue to, among other things, the frequency response of the variouscomponents of the RF transmitter 14. In other words, as the sweep signalfrequency is swept, the various amplifiers may provide slightly varyinglevels of amplification and the various attenuators may provide slightlyvarying levels of attenuation. The feedback control loop provided by thefeedback detector 322, the control loop amplifier 326 and the variableattenuator 318 ensures that a constant output level is maintainedthroughout the swept frequencies of the output sweep signal. It is notedthat the feedback control loop may further contain temperaturecalibration control circuitry, the implementation of which would beknown to those of ordinary skill in the art.

The resistor network 350 receives the sweep signal from the RF output310 and provides the sweep signal to the broadband detector 352 of themeasurement circuit 16 and to the coupling device 13. Furthermore, theresistor network 350 receives reflected sweep signals from the couplingdevice 13 and provides the received reflected sweep signals to the DCbroadband detector 352. Depending on the state of the coupling device13, the resistor network 350 receives the reflected sweep signals fromeither the first impedance device 17a or the subscriber networkconnected to the RF connector 12.

The DC broadband detector 352 generates a DC voltage that is indicativeof the magnitude of the signal received from the resistor network 350.Since the resistor network 350 provides the DC broadband detector 352with a resultant signal that includes the sweep signal and the reflectedsweep signal, the DC broadband detector 352 generates a DC voltage thatis indicative of the received resultant signal. The DC broadbanddetector 352 then provides the DC voltage to the capacitor 354. Thecapacitor 354 helps reduce any AC components that may exist in the DCvoltage. In other words, the capacitor 354 helps to filter out anyflutter, drift, or spikes that may be generated by the DC broadbanddetector 352. The filtered DC voltage is then provided to the amplifier356 which generates a measurement signal that is an amplified version ofthe filtered DC voltage. The main purpose of the amplifier 356 is toprovide the A/D converter 18 with a measurement signal that has a broadenough voltage range for the A/D converter 18 to accurately detectdifferences in generated measurement signals.

From a received measurement signal, the A/D converter 18 generates an8-bit digital value that is indicative of the DC level of the receivedmeasurement signal. The A/D converter 18 then provides the digital valueto the DSP/controller 20 for processing. In general, the DSP/controller20 executes algorithms stored in the memory 21 which cause thereflectometer 10 to display severity and location of impedancemismatches in the subscriber network under test. To this end, theDSP/controller 20 obtains a reflected sweep response signal for thesubscriber network. The DSP/controller 20 then obtains a reflected sweepresponse spectrum that includes a plurality of spectral peaks thatindicates severity and location of impedance mismatches. TheDSP/controller 20 adjusts the spectral peaks for loss due to attenuationin the subscriber network. Furthermore, the DSP/controller 20 suppressesspectral peaks that are harmonics of other spectral peaks. Finally, theDSP/controller 20 causes severity and location information of impedancemismatches within the subscriber network under test to be displayed onthe display 26.

Further details of the operation of the reflectometer 10 and theDSP/controller 20 are discussed with reference to FIGS. 4A, 4B, and 4C.Shown in FIGS. 4A, 4B, and 4C is a detailed reflectometry procedure 400which illustrates various features of the present invention. Thereflectometry procedure 400 begins in step 402 with a user providing thereflectometer 10 with various parameters. In particular, the user of theembodiment described herein enters a velocity of propagation constantVop for the subscriber network under test, an attenuation factor α forthe subscriber network, and selects a sweep resolution swp₋₋ res for thedetection of impedance mismatches in subscriber network. Furthermore,the user may select harmonic suppression to be applied to the reflectedsweep response signal.

To this end, the user enters a first value for the velocity ofpropagation constant Vop for the transmission line 24 under test and asecond value for attenuation factor α which represents the attenuationfactor in dB per 100 feet of the transmission line 24 for 50 MHz signal.It should be noted that the first value for velocity of propagationconstant Vop and the second value for attenuation factor α may bereadily obtained from published characteristics of the coaxial cableswhich comprise the subscriber network. Furthermore, the user sets thesweep resolution swp₋₋ res by selecting between four predefined sweepresolutions swp₋₋ res. In particular, the exemplary embodiment describedherein includes the following sweep resolutions: an ultra sweepresolution (swp₋₋ res=1024 sweep segments), a maximum sweep resolution(swp₋₋ res=512 sweep segments), a medium sweep resolution (swp₋₋ res=256sweep segments), and a minimum sweep resolution (swp₋₋ res=128 sweepsegments). As a result of setting the sweep resolution swp₋₋ res, thenumber of spectral peaks FDR₋₋ pks is also set. The spectral peaks FDR₋₋pks are the number of spectral peaks resulting from spectral analysis ofthe reflected sweep response signal disregarding the spectral peakscorresponding to negative frequencies. As a result, the spectral peaksFDR₋₋ pks are equal to the number of sweep segments divided by 2. Forexample, spectral analysis of the reflected sweep response signal willyield 512 spectral peaks in the ultra sweep resolution mode since theultra sweep resolution mode contains 1024 sweep segments.

The exemplary embodiment described herein also includes four predefinedzoom factors that alter the sweep span of the four predefined sweepresolutions. Each zoom factor that alters the sweep span has apredefined start frequency Fstart and a predefined stop frequency Fstopfor each predefined sweep resolution. As a result of selecting a sweepresolution swp₋₋ res and a zoom factor, the DSP/controller 20 maydetermine other parameters which characterize the reflectometryprocedure 400 to be performed. For example, the DSP/controller 20 maydetermine a frequency span ("freq₋₋ span") in MHz and a frequencyincrement ("freq₋₋ inc") in MHz for the sweep signal from the followingequations. ##EQU3## It should be noted that a reflectometer whichincorporates features of the present invention may be implementedwithout being limited to four sweep resolutions and four zoom factors.For example, the reflectometer 10 may be implemented such that the userenters a value for the sweep resolution swp₋₋ res, a value for a maximumdistance max₋₋ dist at which to detect an impedance mismatch, and avalue for the start frequency Fstart. For such information, theDSP/controller 20 may determine values for a distance resolution dist₋₋res in feet per segment, a frequency span freq₋₋ span in MHz, a stopfrequency Fstop in MHz, and frequency increment freq₋₋ inc in MHz fromthe following equations: ##EQU4## The above are solely for exemplarypurposes. One skilled in the art may devise other minimal sets ofparameters that must be supplied by the user performing thereflectometry procedure 400.

After obtaining the above parameters, the reflectometer 10 proceeds tostep 406 wherein the DSP/controller 20 performs parameter validation. Inparticular, the DSP/controller 20 determines whether any of theparameters are outside of acceptable ranges for the reflectometer 10. Ifa parameter is outside of an acceptable range, then the reflectometer 10returns to step 402 to receive valid parameters. To this end, theDSP/controller 20 determines whether the first value for the propagationconstant Vop is between 0.01 and 0.99 and the second value for theattenuation factor α is between 0.0 and 3.5. Furthermore, thereflectometer 10 may need to perform other parameter validations if thereflectometer 10 is not limited to predefined sweep resolutions and zoomfactors. For example, the reflectometer 10 may need to determine whethera supplied maximum distance max₋₋ dist falls between a minimum value forthe maximum distance and maximum distance supported by the reflectometer10.

If the parameters are valid, then the reflectometer 10 proceeds to step408 in order to obtain a reference sweep response signal. To this end,the DSP/controller 20 generates a control signal which causes thecoupling device 13 to connect the first impedance device 17a to the RFtransmitter 14 and the measurement circuit 16. Furthermore, in responseto the control signal, the coupling device 13 connects the secondimpedance device 17b to the RF connector 12 in order to maintain propertermination of the system under test. After the reflectometer 10 isconfigured for a reference sweep, the reflectometer 10 performs areference sweep upon the reference impedance 17 in step 410. Inparticular, the DSP/controller 20 generates control signals which causethe RF transmitter to generate a sweep signal having a first segment atthe start frequency (Fstart), a second segment at the start frequencyplus the frequency increment (Fstart+freq₋₋ inc), a third segment at thestart frequency plus two times the frequency increment (Fstart+2*freq₋₋inc), and so on, and including the final segment at the stop frequency(Fstop).

In response to generation of the reference sweep signal, the measurementcircuit 16 obtains a separate reference measurement for each segment. Inparticular, the measurement circuit 16 generates for each segment ameasurement signal having a DC level that is representative of themagnitude of the resultant sweep response signal for the segment. Themeasurement circuit 16 then provides each measurement signal to the A/Dconverter 18 for digitizing. The A/D converter 18 then digitizes eachmeasurement signal and provides each digitized measurement signal to theDSP/controller 20 which causes each measurement signal to be stored inthe memory 21 for future access. In a preferred embodiment, themeasurement circuit 16 provides the A/D converter 18 with eightmeasurement signals for each segment of the reference sweep signal whichare later averaged and stored by the DSP/controller 20. The averaging ofmultiple measurements at each segment of the reference sweep signalhelps to reduce noise in the reference sweep response signal. Anexemplary reference sweep response signal is shown in FIG. 5. Asdepicted, the reference sweep response signal tends to have a slightupward slope due to the hardware which implements the measurementcircuit 16.

After the reference sweep response has been obtained, the reflectometer10 is configured in step 412 for a test sweep. To this end, theDSP/controller 20 generates a control signal which causes the couplingdevice 13 to couple the system under test to the RF transmitter 14 andthe measurement circuit 16. After the reflectometer 10 is configured fora test sweep, the reflectometer 10 performs in step 414 a test sweepupon the subscriber network under test. To this end, the DSP/controller20 generates control signals which cause the RF transmitter to generatea test sweep signal having the same characteristics as the referencesweep signal of step 410. In particular, the DSP/controller 20 generatescontrol signals which cause the RF transmitter to generate a test sweepsignal having a first segment at the start frequency (Fstart), a secondsegment at the start frequency plus the frequency increment(Fstart+freq₋₋ inc), a third segment at the start frequency plus twotimes the frequency increment (Fstart+2*freq₋₋ inc), and so on until thefinal segment at the stop frequency (Fstop).

The measurement circuit 16 in response to generation of the test sweepsignal obtains a separate test measurement for each segment. Inparticular, the measurement circuit 16 generates for each segment ameasurement signal having a DC level that is representative of themagnitude of the resultant sweep signal for the segment. The resultantsweep signal includes the incident test sweep signal transmitted by theRF transmitter 14 plus any reflected test sweep signal reflected by thesubscriber network under test. The measurement circuit 16 then provideseach measurement signal to the A/D converter 18 for digitizing. The A/Dconverter 18 then digitizes each measurement signal and provides theeach digitized measurement signal to the DSP/controller 20 which causeseach measurement signal to be stored in the memory 21 for future access.In a preferred embodiment, the measurement circuit 16 provides the A/Dconverter 18 with eight measurement signals for each segment of the testsweep signal which are averaged and stored by the DSP/controller 20. Theaveraging of multiple measurements at each segment of the resultantsweep response signal helps to reduce noise in the resultant sweepresponse signal. An exemplary resultant sweep response signal thatincludes the incident and reflected test sweep signal is shown in FIG. 6for an unterminated 27 foot cable.

After the test sweep response signal is obtained, the reflectometer 10extracts the reflected sweep response signal from the resultant sweepresponse signal. To this end, the DSP/controller 20 divides themeasurement signal for each segment of the test sweep response signal bythe measurement signal for the corresponding segment of the referencesweep response signal. Furthermore, from this resulting signal theDSP/controller 20 subtracts the value of 1 from each point of theresulting signal in order to obtain the difference between the resultantsweep response signal and the reference sweep response signal. In sum,the extraction of the reflected sweep response signal may be representedby the following equation: ##EQU5## where A_(x) is the measurement levelof the x^(th) segment of the reference sweep response signal, B_(x) isthe measurement level of the x^(th) segment of the test sweep responsesignal, and C_(x) is the level of the x^(th) segment of the reflectedsweep response signal. FIG. 7 shows a reflected sweep response signalfor an unterminated 27 foot transmission line. Since each point of thereflected sweep response signal is representative of the response of thetransmission line to a test signal having a certain frequency, thereflected sweep response signal is essentially a frequency response ofthe transmission line under test.

After the reflectometer 10 obtains the reflected sweep response signal,the reflectometer 10 performs spectral analysis upon the reflected sweepresponse signal in order to obtain a reflected sweep response spectrumthat includes a plurality of spectral peaks FDR₋₋ pks which representthe frequency components of the reflected sweep response signal. Inparticular, the DSP/controller 20 applies in step 420 a windowingtechnique (e.g. a Hamming window) to the reflected sweep response signaland performs in step 422 a Fast Fourier Transform ("FFT") upon theresults of the windowing technique. The effect of the windowingtechnique is to yield a cleaner spectrum when the FFT is applied to thereflected sweep response signal. FFT techniques and windowing techniquesare well known to those of ordinary skill in the art.

The FFT yields a reflected sweep response spectrum having a plurality ofspectral peaks FDR₋₋ pks in which each spectral peak includes amagnitude and a frequency. The magnitude of a spectral peak indicatesseverity of a possible impedance mismatch within the subscriber network.Furthermore, the frequency of the spectral peak indicates location of apossible impedance mismatch within the subscriber network. It should benoted that the FFT of the reflected sweep response signal will generatespectral peaks having both positive and negative frequencies. TheDSP/controller 20 in the exemplary embodiment described herein discardseach spectral peak that has a negative frequency thereby reducing thenumber of points in the spectrum by half. For example, in the ultrasweep resolution mode, the test sweep signal has 1024 segments thatgenerates a reflected sweep response signal having 1024 points. However,when the FFT is applied to the reflected sweep response signal, the FFTgenerates a reflected sweep response segment having 512 spectral peaksranging from a first spectral peak FDR₋₋ pk₁ to a last spectral peakFDR₋₋ pk₅₁₂. An exemplary reflected sweep response spectrum 62 is shownin FIG. 1, and a simplified exemplary reflected sweep response spectrumis shown in FIG. 8 for an unterminated 27 foot transmission line. Itshould be noted that the reflected sweep response spectrum isessentially the frequency components of the frequency response of thetransmission line under test.

The DSP/controller 20 then scales each point of the reflected sweepresponse signal in order to (i) compensate for any attenuation or gainthe reflectometer 10 has introduced into the signal measurement and (ii)relate the reflected sweep response signal to the magnitude of returnloss due to an impedance mismatch in the subscriber network reflectingback the test sweep signal. In particular, the magnitude of return lossin dB may be represented by the following equation:

    |Return.sub.-- Loss|=20·log(Rpp)

where Rpp is the peak to peak value of the reflected sweep responsesignal. As a result of the above, the DSP/controller 20 multiplies eachpoint of the reflected sweep response signal by a circuit compensationfactor ckt₋₋ comp in order to compensate for the reflectometer 10 and by20 in order to relate the reflected sweep response signal to themagnitude of return loss.

The reflectometer 10 then proceeds to step 424 wherein theDSP/controller 20 adjusts the obtained spectrum for effects due toattenuation in the subscriber network. In general, the DSP/controller 20determines a separate attenuation compensation factor for each spectralpeak of the spectrum and multiplies the magnitude of each spectral peakby its corresponding correction factor in order to obtain a reflectedsweep response spectrum that has been compensated for attenuation. FIG.4B illustrates an attenuation compensation procedure 450 whichincorporates various features of the present invention therein.

In order to better appreciate the attenuation compensation procedure 450of the present invention, a detailed explanation of attenuation effectsfollows. The attenuation factor α for a transmission line determines theamount of energy dissipated in the transmission line. The primary causeof attenuation is due to conductor losses associated with radiofrequencies. These conductor losses are a function of distance traveledthrough the conductor and of skin depth and hence vary with the squareroot of frequency. The attenuation factor α for a transmission line maybe represented by the following equations: ##EQU6## where σ equals theconductance loss of the transmission line, d equals distance traveledthrough the transmission line, and freq equals frequency of the RFsignal traveling through the transmission line.

Ideally, a single impedance mismatch within the subscriber network willreflect a single sinusoid at a given frequency. However, attenuation inthe subscriber network will have a dampening effect on the magnitude ofthe reflected sinusoid. This dampening effect may be represented by asingle sinusoid multiplied by the attenuation factor α. Therefore, areflected sweep segment as a function of the frequency freq of a singlesweep segment may be depicted by the following equation: ##EQU7## whereα equals attenuation factor for a transmission line at the frequencyfreq, A equals the amplitude of the reflected sweep signal, freq equalsthe frequency of the reflected sweep signal, dist equals the distance ofthe impedance mismatch from the reflectometer 10, Vop equals thevelocity of propagation for the transmission line, and 491 is 1/2 thespeed of light in feet per a microsecond. Substituting t for freq, f1for (dist/(Vop*491)), and c for the constant 491, the above equation maybe rewritten as follows: ##EQU8##

The ideal response without attenuation would be the FFT of a cosinewhich is an impulse (dirac) function with an amplitude of 1/2A at afrequency equal to f1. The FFT of two functions multiplied together inthe time domain is equal to the FFT of the first function convolutedwith the FFT of the second function. Therefore the above function can berewritten as follows: ##EQU9##

Convolution with the impulse function δ(f1) shifts the FFT of theattenuation factor to the frequency f1. Therefore, the FFT of thereflected segment may be represented by the following equation:##EQU10## As can be seen from the above equation, the FFT of theattenuation factor determines the effect of attenuation on oneparticular spectral peak FDR₋₋ pk_(x) of the reflected sweep responsespectrum. The FFT of the attenuation factor, however, does not have aclosed form but can be solved point to point and is graphically shown inFIG. 10. FIG. 10 illustrates that the major effect of the attenuationfactor is centered at 0 on the X-axis (i.e. the DC component) and decaysquite rapidly. The rate of decay determines the effects on otherspectral peaks near the one particular spectral peak FDR₋₋ pk_(x). Ifthe magnitude of the spectral peak is sufficiently large, then thespectral peak may be approximated by an impulse at DC without concernfor the spreading effects. The rate of decay is determined by theattenuation factor for the transmission line. For large values ofattenuation, the graph of the FFT of the attenuation factor will bewider and effect other spectral peaks. These effects on other spectralpeaks will not add appreciable error in a CATV system since cableattenuation must be within a reasonable range in order for the CATVsystem to function properly.

The amplitude of the above impulse at DC is the inverse of theattenuation compensation factor α₋₋ comp_(x) that needs to be applied tothe magnitude of the spectral peak FDR₋₋ pk_(x). The amplitude of theabove impulse at DC is the simple average of the attenuation for thedistance dist across the frequency span freq₋₋ span which is expressedby the following equation: ##EQU11## where f is incremented between thestart frequency Fstart and the stop frequency Fstop of the test sweep bythe frequency increment freq₋₋ inc of the test sweep. Taking the inverseof the above DC equation and substituting the above distance equation Dinto the above DC equation, the attenuation compensation factor α₋₋comp_(x) for a spectral peak FDR₋₋ pk_(x) having a spectral frequencyf_(R).sbsb.x, is defined by the following equation: ##EQU12## where f isincremented between the start frequency Fstart of the test sweep and thestop frequency Fstop of the test sweep by the frequency increment freq₋₋inc of the test sweep.

The DSP/controller 20 could determine the conductance loss σ for thesubscriber network from the attenuation factor α supplied by the user instep 402. Then, the DSP/controller 20 could calculate from the aboveattenuation compensation factor equation an appropriate attenuationcompensation factor for each spectral peak of the reflected sweepresponse spectrum. In particular, since the user supplied theattenuation factor α for the subscriber network in dB per 100 ft for asignal having a frequency of 50 MHz, the DSP/controller 20 may apply thesupplied attenuation factor α to the following equation to obtain theconductance loss σ for subscriber network. ##EQU13## Then, theDSP/controller 20 may determine an attenuation compensation factor α₋₋comp_(x) for each spectral peak FDR₋₋ pk_(x) of the reflected sweepresponse spectrum by calculating the attenuation compensation factor α₋₋comp_(x) from the above attenuation compensation factor equation α₋₋comp_(x) (f_(R).sbsb.x). It should be noted that this approach iscomputationally intensive, especially in the ultra mode where theDSP/controller 20 may need to calculate a separate attenuationcompensation factor α₋₋ comp_(x) for each of the 512 spectral peaks ofthe reflected sweep response spectrum.

Therefore, in order to reduce the computation burden of theDSP/controller 20, the reflectometer 10 of the exemplary embodimenttakes advantage of the fact that the logarithm of the attenuationcompensation factor equation α₋₋ comp_(x) (f_(R).sbsb.x) exhibitspiece-wise linear characteristics. As a result of these piece-wiselinear characteristics, the DSP/controller 20 may linearly interpolateattenuation compensation factors α₋₋ comp from a few provided orcalculated attenuation compensation factors. In particular, since theexemplary embodiment supports a limited number of predefined sweepresolutions and zoom factors, the reflectometer 10 stores a table ofattenuation compensation factors from which to interpolate additionalattenuation compensation factors.

As can be seen from the above attenuation compensation factor equation,the attenuation compensation factor equation is dependent on the sweepresolution, the zoom factor, and the velocity of propagation constantVop times the conductance loss σ. As a result of these dependency,separate attenuation compensation factors must be stored for each sweepresolution, zoom factor, and velocity of propagation constant Vop timesconductance loss σ values supported by the reflectometer 10. It has beendetermined that the reflectometer 10 of the exemplary embodiment mayobtain a desired level of accuracy by supplying an attenuationcompensation table of attenuation compensation factors that takes intoaccount 101 different velocity of propagation constant Vop timesconductance loss σ values that range between and include the values 0.0and 0.5.

For example, in the exemplary embodiment, the reflectometer 10 supports16 sweep modes made up of 4 sweep resolutions that each have 4 zoomfactors that alter the start frequency Fstart and the stop frequencyFstop of the test sweep signal. Accordingly, for each of the 16 sweepmodes, the attenuation compensation table includes 101 middleattenuation compensation factors α₋₋ comp_(mid) and 101 end attenuationcompensation factors α₋₋ comp_(end). Each of the 101 attenuationcompensation factor pairs corresponds to a different velocity ofpropagation constant Vop times conductance loss σ value. In particular,each end compensation factor α₋₋ comp_(end) corresponds to a maximumspectral frequency f_(R).sbsb.max obtainable for the sweep mode with itsrespective velocity of propagation constant Vop times conductance loss σvalue. Similarly, each middle compensation factor α₋₋ comp_(mid)corresponds to a middle spectral frequency f_(R).sbsb.mid that is halfof the maximum spectral frequency f_(R).sbsb.max obtainable for thesweep mode with its respective velocity of propagation constant Voptimes conductance loss σ value. Furthermore, in the exemplaryembodiment, each attenuation compensation factor is a two byte value.Accordingly, the attenuation compensation table of the exemplaryembodiment contains 6,464 bytes (16 modes*101 pairs/mode*4 bytes/pair)of attenuation compensation factors.

Now referring back to FIG. 4B, the attenuation compensation procedure450 will be described in detail. In order to simplify the followingdescription, it is assumed that the FFT in step 416 produced 512spectral peaks ranging from a first spectral peak FDR₋₋ pk₁ to a lastspectral FDR₋₋ pk₅₁₂. The attenuation compensation procedure 450 beginsin step 452 with the DSP/controller 20 obtaining the first spectral peakFDR₋₋ pk₁ of the reflected sweep response spectrum. The DSP/controller20 then determines in step 454 whether the magnitude of the selectedspectral peak FDR₋₋ pk_(x) is greater than a noise floor level for thereflectometer 10. If the magnitude of the selected spectral peak FDR₋₋pk_(x) is not greater than the noise floor level, the DSP/controller 20proceeds to step 464 in order to determine whether the last spectralpeak FDR₋₋ pk₅₁₂ has been processed. If the DSP/controller 20 determinesthat the last spectral peak FDR₋₋ pk₅₁₂ has not been processed then theDSP/controller 20 proceeds to step 466 to obtain the next spectral peakFDR₋₋ pk_(x+1) for processing.

If the magnitude of the selected spectral peak FDR₋₋ pk_(x) is greaterthan the noise floor level, then the DSP/controller 20 proceeds to step456. In step 456, the DSP/controller 20 determines whether the frequencyf_(R).sbsb.x of the selected spectral peak FDR₋₋ pk_(x) is less than orequal to the middle spectral frequency f_(R).sbsb.mid for the testsweep. If the frequency f_(R).sbsb.x is less than or equal to the middlespectral frequency f_(R).sbsb.mid for the test sweep, then theDSP/controller 20 proceeds to step 458; otherwise the DSP/controller 20proceeds to step 460. In step 458, the DSP/controller 20 obtains themiddle attenuation compensation factor α₋₋ comp_(mid) for the test sweepfrom the attenuation compensation table. In particular, theDSP/controller 20 obtains the middle attenuation compensation factor α₋₋comp_(mid) that corresponds to (i) the sweep resolution and the zoomfactor of the test sweep and (ii) that most closely matches the velocityof propagation Vop times the conductance loss σ value for the subscribernetwork supplied by the user in step 402. The DSP/controller 20 then instep 459 determines the attenuation compensation factor α₋₋ comp_(x) forthe selected spectral peak FDR₋₋ pk_(x) from the obtained middleattenuation compensation factor α₋₋ comp_(mid). In particular, theDSP/controller 20 applies the middle attenuation compensation factor α₋₋comp_(mid) to the following equation in order to obtain the attenuationcompensation factor α₋₋ comp_(x) for the selected spectral peak FDR₋₋pk_(x). ##EQU14## where max₋₋ dist equals the maximum distance for thesweep mode, and dist_(x) equals the distance corresponding to FDR₋₋pk_(x). It should be noted the 1/2 max₋₋ dist is equal to the distanceassociated with the middle attenuation compensation factor α₋₋comp_(mid).

In step 460 the DSP/controller 20 obtains from the attenuationcompensation table the middle attenuation compensation factor α₋₋comp_(mid) and the end attenuation compensation factor α₋₋ comp_(end)for the test sweep. The DSP/controller 20 then in step 461 determinesthe attenuation compensation factor α₋₋ comp_(x) for the selectedspectral peak FDR₋₋ pk_(x) from the obtained middle attenuationcompensation factor α₋₋ comp_(mid) and the obtained end attenuationcompensation factor α₋₋ comp_(end). In particular, the DSP/controller 20applies the obtained middle attenuation compensation factor α₋₋comp_(mid) and the obtained end attenuation compensation factor α₋₋comp_(end) to the following equation in order to obtain the attenuationcompensation factor α₋₋ comp_(x) for the selected spectral peak FDR₋₋pk_(x). ##EQU15## where max₋₋ dist equals the maximum distance for thesweep resolution mode, and dist_(x) equals the distance corresponding toFDR₋₋ pk_(x). It should be noted the 1/2 max₋₋ dist is equal to thedistance associated with the middle attenuation compensation factor α₋₋comp_(mid).

In either event, the DSP/controller 20 adjusts in step 463 the magnitudeof the selected spectral peak FDR₋₋ pk_(x). In particular, theDSP/controller 20 multiplies the magnitude of the selected spectral peakFDR₋₋ pk_(x) by the obtained attenuation compensation factor α₋₋comp_(x) for the selected spectral peak FDR₋₋ pk_(x) in order to obtainan adjusted magnitude for the selected spectral peak FDR₋₋ pk_(x). Oncethe DSP/controller 20 has adjusted the magnitude of the selectedspectral peak FDR₋₋ pk_(x), the DSP/controller 20 proceeds to step 464.In step 464, the DSP/controller 20 determines whether the last spectralpeak FDR₋₋ pk₅₁₂ has been processed. If the last spectral peak FDR₋₋pk₅₁₂ has been processed, then the DSP/controller 20 finishes theattenuation compensation procedure 450 by proceeding to step 426 of thereflectometry procedure 400 shown in FIG. 4A. However, if the lastspectral peak FDR₋₋ pk₅₁₂ has not been processed, then theDSP/controller 20 proceeds to step 466. In step 466, the DSP/controller20 selects the next spectral peak FDR₋₋ pk_(x+1) for processing. Forexample, if the DSP/controller 20 was processing the 20^(th) spectralpeak FDR₋₋ pk₂₀, then the DSP/controller 20 selects the 21^(st) spectralpeak FDR₋₋ pk₂₁ as the next spectral peak. After selecting the nextspectral peak the DSP/controller 20 returns to step 454 in order toprocess the selected spectral peak.

After the reflectometer 10 compensates the spectral peaks of thereflected sweep response signal for attenuation effects, thereflectometer 10 performs a distance calculation for each spectral peak.To this end, the DSP circuit 10 determines a distance dist for eachspectral peak FDR₋₋ pk_(x) of the reflected sweep response spectrum fromthe above distance equation which for convenience is also presentedbelow: ##EQU16## where f_(R) equals the frequency of a spectral peak ofthe reflected sweep response spectrum, c is the speed of light in feetper microsecond, and Vop is the velocity of propagation which the usersupplied in step 402.

The reflectometer 10 then in step 428 suppresses the spectral peaks thatare harmonics of other spectral peaks. In general, the DSP/controller 20determines whether a first spectral peak has a predeterminedrelationship to a second spectral peak that is indicative of the firstspectral peak being a harmonic of the second spectral peak. If theDSP/controller 20 determines the first spectral peak has thepredetermined relationship then the DSP/controller 20 subtracts apercentage of the magnitude of the second spectral peak from themagnitude of the first spectral peak.

To this end, the DSP/controller 20 obtains a first maximum magnitudefrom a first group of spectral peaks that fall within a first harmonicwindow of a first spectral peak. The DSP/controller 20 then multipliesthe obtained first maximum magnitude by a first harmonic factor in orderto obtain a first harmonic value that is indicative of a first harmoniccomponent contained in the first spectral peak. Then, the DSP/controller20 obtains a second maximum magnitude from a second group of spectralpeaks that fall within a second harmonic window of the first spectralpeak. The DSP/controller 20 then multiplies the obtained second maximummagnitude by a second harmonic factor in order to obtain a secondharmonic value that is indicative of the second harmonic componentcontained in the first spectral peak. Finally, the DSP/controller 20subtracts the greater of the first harmonic value and the secondharmonic value from the first spectral peak in order to remove therespective harmonic component from the first spectral peak.

A detailed harmonic suppression procedure 470 which incorporates variousfeatures of the present invention therein is illustrated in FIG. 4C. Inorder to better appreciate the harmonic suppression procedure 470 of thepresent invention, a detailed explanation of harmonics follows.

The equation for a wave on a transmission line is as follows: ##EQU17##where Z₀ equals the characteristic impedance √Z/Y; √Z·Y equals thepropagation constant α+j·β; E_(G) equals the voltage at the generator ofthe wave, E_(R) equals the voltage at the load, I_(R) equals the currentat the load, and L equals the length of the transmission line. As can beseen from the above equation, the general response of a wave on atransmission line over distance contains hyperbolic functions cosh andsinh. As a result of the hyperbolics, the response contains harmonicsthat depend primarily on the severity of the impedance mismatch, theattenuation constant, and the distance to fault.

As shown in FIG. 7, the reflected sweep signal response for anunterminated 27 foot transmission line may be represented by ahyperbolic cosine function. As a result of the reflected sweep signalresponse being hyperbolic, spectral analysis of the reflected sweepresponse signal yields the reflected sweep response spectrum shown inFIG. 8 and shown in greater detail in FIG. 9. As shown in FIG. 9, thereflected sweep response spectrum has a fundamental spectral peak FDR₋₋pk_(f0) having a frequency f_(R) at a distance of approximately 27 feet.The reflected sweep response also includes (i) a first harmonic spectralpeak FDR₋₋ pk_(f1) having a frequency of 2*f_(R) at 54 feet which is afirst harmonic of the fundamental spectral peak, and a second harmonicspectral peak FDR₋₋ pk_(f2) having a frequency of 3*f_(R) at 81 feetwhich is a second harmonic of the fundamental spectral peak.

Since the first harmonic spectral peak FDR₋₋ pk_(f1) and the secondharmonic spectral peak FDR₋₋ pk_(f2) may falsely be interpreted asfaults in the transmission line, the present invention attempts toremove or suppress first harmonic spectral peaks FDR₋₋ pk_(f1) andsecond harmonic spectral peaks FDR₋₋ pk_(f2) of the reflected sweepresponse spectrum. The reflected sweep response spectrum may alsoinclude third, fourth, fifth, etc. harmonic spectral peaks. However,these higher harmonic spectral peaks tend to have sufficiently smallenough magnitudes that they will not be mistaken as faults. Accordingly,these higher harmonic spectral peaks may typically be ignored. It shouldbe noted, however, that the present invention could easily be extendedto suppress these higher harmonics as well.

Furthermore, as shown in FIG. 9, from the standpoint of the secondharmonic spectral peak FDR₋₋ pk_(f2), the fundamental spectral peakFDR₋₋ pk_(f0) falls within a second harmonic window of the secondharmonic spectral peak FDR₋₋ pk_(f2). Likewise, the first spectral peakFDR₋₋ pk_(f1) falls within a first harmonic window of the secondharmonic spectral peak FDR₋₋ pk_(f2). It should be noted that the secondharmonic spectral peak FDR₋₋ pk_(f2) may be thought of as a firstharmonic of the first harmonic spectral peak FDR₋₋ pk_(f1).

Referring back to FIG. 4C, the harmonic suppression procedure 470 beginsin step 472 with the DSP/controller 20 selecting the last spectral peak(i.e. the spectral peak corresponding to the greatest distance from thereflectometer 10). The DSP/controller 20 then determines in step 474whether the magnitude of the selected spectral peak is greater than thenoise floor for the reflectometer 10. If the magnitude of the selectedspectral peak is greater than the noise floor, then the reflectometer 10proceeds to step 476. However, if the selected spectral peak is lessthan the noise floor, then the reflectometer 10 proceeds to step 486where the reflectometer 10 determines whether any more spectral peaksare available for processing. If the reflectometer 10 determines in step486 that the harmonic suppression procedure 470 has yet to reach thefirst spectral peak (i.e. the spectral peak corresponding to theshortest distance from the reflectometer 10), then the reflectometer 10proceeds to step 488 to obtain the spectral peak preceding the justprocessed spectral peak.

Once the DSP/controller 20 obtains a first spectral peak above the noisefloor, the DSP/controller 20 determines whether the first spectral peakhas a first relationship to a second spectral peak that is indicative ofthe first spectral peak being a first harmonic of the second spectralpeak. To this end, the first DSP/controller 20 determines in step 476whether a spectral peak above the noise floor exists in a first harmonicwindow of the first spectral peak. The first harmonic window includes asecond spectral peak that corresponds to the distance of the firstspectral peak divided by two. It should be noted that the first harmonicof a fundamental spectral peak occurs at a distance equal to twice thedistance or twice the frequency of the fundamental spectral peak. As aresult, if the first spectral peak is a first harmonic of the secondspectral peak, then the second spectral peak should be located at thedistance of the first spectral peak divided by two. However, due to theresolution of the test sweep signal and various other inaccuracies, thefundamental spectral peak may not fall exactly at the distance of thefirst spectral peak divided by two. Accordingly, the first harmonicwindow also includes the two spectral peaks to each side of the secondspectral peak in order to account for the test sweep resolution andother inaccuracies.

The DSP/controller 20 then obtains a first maximum magnitude of thefirst group of spectral peaks that fall within the first harmonicwindow. If the first maximum magnitude is greater than the noise floor,then the first maximum magnitude is likely the magnitude of thefundamental spectral peak of the first spectral peak. Accordingly, theDSP/controller 20 determines in step 478 the likely effect the spectralpeak corresponding to the first maximum magnitude had on the magnitudeof the first spectral peak. To this end, the DSP/controller 20multiplies the first maximum magnitude by a first harmonic factor inorder to obtain a first harmonic value that is indicative of a firstharmonic component contained in the first spectral peak. It should benoted that the first harmonic of a fundamental has a magnitude that is14 dB down from the magnitude of the fundamental or that is 0.2 of themagnitude of the fundamental. As a result, the DSP/controller 20multiplies the first maximum magnitude by 0.2 in order to obtain thefirst harmonic value. However, if the second maximum magnitude is notgreater than the noise floor, then the DSP/controller 20 sets the firstharmonic value equal to zero thus indicating that the first spectralpeak is not a first harmonic of another spectral peak.

The DSP/controller 20 then determines whether the first spectral peakhas a second relationship to a third spectral peak that is indicative ofthe first spectral peak being a second harmonic of the third spectralpeak. To this end, the DSP/controller 20 determines in step 480 whethera spectral peak above the noise floor exists in a second harmonic windowof the first spectral peak. The second harmonic window includes a thirdspectral peak that corresponds to the distance of the first spectralpeak divided by three. It should be noted that the second harmonic of afundamental spectral peak occurs at a distance equal to thrice thedistance or thrice the frequency of the fundamental spectral peak. As aresult, if the first spectral peak is a second harmonic of the thirdspectral peak, then the third spectral peak should be located at thedistance of the first spectral peak divided by three. However, due tothe resolution of the test sweep signal and various other inaccuracies,the fundamental spectral peak may not fall exactly at the distance ofthe first spectral peak divided by three. Accordingly, the secondharmonic window also includes the two spectral peaks to each side of thethird spectral peak in order to account for the test sweep resolutionand other inaccuracies.

The DSP/controller 20 then obtains a second maximum magnitude of thesecond group of spectral peaks that fall within the second harmonicwindow. If the second maximum magnitude is greater than the noise floor,then the second maximum magnitude is likely the magnitude of thefundamental spectral peak of the first spectral peak. Accordingly, theDSP/controller 20 determines in step 482 the likely effect the spectralpeak corresponding to the second maximum magnitude had on the magnitudeof the first spectral peak. To this end, the DSP/controller 20multiplies the second maximum magnitude by a second harmonic factor inorder to obtain a second harmonic value that is indicative of a secondharmonic component contained in the first spectral peak. It should benoted that the second harmonic of a fundamental has a magnitude that is21 dB down from the magnitude of the fundamental or that is 0.1 of themagnitude of the fundamental. As a result, the DSP/controller 20multiplies the second maximum magnitude by 0.1 in order to obtain thesecond harmonic value. However, if the second maximum magnitude is notgreater than the noise floor, then the DSP/controller 20 sets the secondharmonic value equal to zero thus indicating that the first spectralpeak is not a second harmonic of another spectral peak.

The DSP/controller 20 then adjusts the magnitude of the first spectralpeak in step 484 to account for the first spectral peak being a harmonicof another spectral peak. To this end, the DSP/controller 20 subtractsthe greater of the first harmonic value and the second harmonic valuefrom the magnitude of the first spectral peak. It should be noted thatthe DSP/controller 20 may subtract the value of zero from the firstspectral peak if neither the first harmonic window or the secondharmonic window contained a spectral peak above the noise floor, thusindicating that the first spectral peak does not contain harmoniccomponents.

After the DSP/controller 20 adjusts the magnitude of the first spectralpeak, the DSP circuit determines in step 486 whether all spectral peakshave been processed by the harmonic suppression procedure 470. To thisend, the DSP/controller 20 determines whether the spectral peakcorresponding to the smallest frequency or the shortest distance hasbeen processed. If this spectral peak has yet to be been processed, thenthe DSP/controller 20 proceeds to step 488 in order to obtain anotherspectral peak for processing. Otherwise, the reflectometer 10 finishesthe harmonic suppression procedure 470 by proceeding to step 430 of thetransmission line analysis procedure 400.

In step 488, the DSP/controller 20 selects the spectral peak immediatelypreceding the spectral peak just processed. For example, if theDSP/controller 20 had just processed the 512^(th) spectral peak FDR₋₋pk₅₁₂, then the DSP/controller 20 selects the 511^(th) spectral peakFDR₋₋ pk₅₁₁ for processing. After selecting another spectral peak forprocessing, the DSP/controller 20 returns to step 474 in order toprocess the selected spectral peak.

It will be appreciated that the above described embodiments are merelyillustrative, and that those of ordinary skill in the art may readilydevise their own implementations that incorporate the features of thepresent invention and fall within the spirit and scope thereof. Forexample, one skilled in the art may implement the DSP/controller 20 withvarious analog and/or digital circuit components that provide thefunctionality of the DSP/controller 20. Specifically, the DSP/controller20 may be implemented to include a spectral analyzer circuit operable toobtain frequency components of a reflected sweep response signal, aharmonic suppression circuit operable to suppress harmonics, anattenuation compensation circuit operable to compensate for attenuation,a fault locator circuit operable to determine location of an impedancemismatch, and a severity determining circuit operable to determineseverity of an impedance mismatch. Furthermore, the measurement circuit16 may be replaced with a receiver circuit that is operable to receivethe resultant sweep response circuit and extract the reflected sweepsignal response therefrom.

What is claimed is:
 1. A method of determining severity of impedancemismatches in a system under test, comprising the steps of:applying atest sweep signal to said system under test in order to obtain areflected sweep response signal from said system under test, saidreflected sweep response signal representative of a frequency responseof said system under test; generating from said reflected sweep responsesignal a reflected sweep response spectrum that includes a plurality ofspectral peaks; determining a first attenuation compensation factor fora first spectral peak of said reflected sweep response spectrum, whereinsaid first spectral peak corresponds to a first distance traveledthrough said system under test and said first attenuation compensationfactor accounts for attenuation of a plurality of signals at differentfrequencies traveling said first distance through said system undertest; adjusting said reflected sweep response spectrum for effects dueto attenuation in said system under test in order to obtain an adjustedsweep response spectrum by applying said attenuation compensation factorto a first magnitude of said first spectral peak; and obtaining fromsaid adjusted sweep response spectrum a severity of an impedancemismatch in said system under test.
 2. The method of claim 1, whereinsaid applying step includes the step of:multiplying said first magnitudeof said first spectral peak by said first attenuation compensationfactor.
 3. The method of claim 1, further comprising the stepof:determining that said first magnitude of said first spectral peak isgreater than a noise floor level.
 4. The method of claim 1, wherein saiddetermining step includes the steps of:obtaining a second attenuationcompensation factor for a second distance traveled through said systemunder test; and determining said first attenuation compensation factorby interpolating from said second attenuation compensation factor. 5.The method of claim 1, wherein said determining step includes the stepsof:obtaining from an attenuation compensation table a second attenuationcompensation factor for a second distance traveled through said systemunder test; and determining said first attenuation compensation factorby interpolating from said second attenuation compensation factor. 6.The method of claim 1, wherein said determining step includes the stepsof:calculating a second attenuation compensation factor for a seconddistanced traveled in said system under test; and determining said firstattenuation compensation factor by interpolating from said secondattenuation compensation factor.
 7. The method of claim 1, wherein saiddetermining step includes the step of:calculating said first attenuationcompensation factor by averaging a plurality of attenuation factors forsaid system under test, wherein each attenuation factor of saidplurality of attenuation factors corresponds to said first distance anda different frequency.
 8. The method of claim 1, wherein:said applyingstep includes the step of sweeping said test sweep signal across afrequency span; and said determining step includes the step ofcalculating said first attenuation compensation factor by averaging aplurality of attenuation factors across said frequency span, whereineach attenuation factor of said plurality of attenuation factorscorresponds to said first distance and a different frequency.
 9. Areflectometer for determining severity of impedance mismatches in asystem under test, comprising:a connector configured to couple saidsystem under test to said reflectometer; a transmitter circuit coupledto said connector and configured to apply a test sweep signal to saidconnector and said system under test coupled thereto; a receiver circuitcoupled to said connector and configured to obtain a reflected sweepresponse signal from a resultant response signal that includes (i) saidtest sweep signal from said transmitter circuit and (ii) said reflectedsweep response signal received from said system under test coupled tosaid connector, said reflected sweep response signal representative of afrequency response of said system under test; a spectral analyzercoupled to said receiver circuit, said spectral analyzer configured togenerate from said reflected sweep response signal a reflected sweepresponse spectrum that includes a plurality of spectral peaks; anattenuation compensation circuit coupled to said spectral analyzer, saidattenuation compensation circuit configured to (i) determine a firstattenuation compensation factor for a first spectral peak of saidreflected sweep response spectrum, said first spectral peakcorresponding to a first distance traveled through said system undertest and said first attenuation compensation factor accounting forattenuation of a plurality of signals at different frequencies travelingsaid first distance through said system under test, and (ii) adjust saidreflected sweep response spectrum for effects due to attenuation in saidsystem under test in order to obtain an adjusted sweep response spectrumby applying said attenuation compensation factor to a first magnitude ofsaid first spectral peak; and a severity determining circuit coupled tosaid attenuation compensation circuit and configured to determine aseverity of an impedance mismatch in said system under test from saidadjusted sweep response spectrum.
 10. The reflectometer of claim 9,wherein:said attenuation compensation circuit is further configured tomultiply said first magnitude of said first spectral peak by said firstattenuation compensation factor.
 11. The reflectometer of claim 9,wherein:said attenuation compensation circuit is further configured todetermine that said first magnitude of said first spectral peak isgreater than a noise floor level.
 12. The reflectometer of claim 9,wherein:said attenuation compensation circuit is further configured to(i) obtain a second attenuation compensation factor for a seconddistance traveled through said system under test, and (ii) determinesaid first attenuation compensation factor by interpolating from saidsecond attenuation compensation factor.
 13. The reflectometer of claim9, further comprising an attenuation compensation table that includes asecond attenuation compensation factor for a second distance traveledthrough said system under test, wherein:said attenuation compensationcircuit is further configured to (i) obtain said second attenuationcompensation factor from said attenuation compensation table, and (ii)determine said first attenuation compensation factor by interpolatingfrom said second attenuation compensation factor.
 14. The reflectometerof claim 9, wherein:said attenuation compensation circuit is furtherconfigured to calculate said first attenuation compensation factor byaveraging a plurality of attenuation factors for said system under test,each attenuation factor of said plurality of attenuation factorscorresponding to said first distance and a different frequency.
 15. Thereflectometer of claim 9, wherein:said transmitter is further configuredto sweep said test sweep signal across a frequency span; and saidattenuation compensation circuit is further configured to calculate saidfirst attenuation compensation factor by averaging a plurality ofattenuation factors across said frequency span, each attenuation factorof said plurality of attenuation factors corresponding to said firstdistance and a different frequency.
 16. A reflectometer for determiningseverity of impedance mismatches in a system under test, comprising:aconnector configured to couple said system under test to saidreflectometer; a transmitter circuit coupled to said connector andconfigured to apply a test sweep signal to said connector and saidsystem under test coupled thereto; a measurement circuit coupled to saidconnector and configured to generate a plurality of measurement signalsindicative of a resultant response signal that includes (i) said testsweep signal from said transmitter circuit and (ii) a reflected sweepresponse signal received from said system under test coupled to saidconnector, said reflected sweep response signal representative of afrequency response of said system under test; an analog to digital (A/D)converter coupled to said measurement circuit and configured to generatefrom said plurality of measurement signals a digitized resultantresponse signal that is a digital representation of said resultantresponse signal; and a digital signal processing (DSP) circuit coupledto said A/D converter, said DSP circuit configured to (i) obtain saidreflected sweep response signal from said digitized resultant responsesignal, (ii) generate from said reflected sweep response signal areflected sweep response spectrum that includes a plurality of spectralpeaks; (iii) determine a first attenuation compensation factor for afirst spectral peak of said reflected sweep response spectrum, saidfirst spectral peak corresponding to a first distance traveled in saidsystem under test and said first attenuation compensation factoraccounting for attenuation of a plurality of signals at differentfrequencies traveling said first distance through said system undertest, (iv) adjust said reflected sweep response spectrum for effects dueto attenuation in said system under test in order to obtain an adjustedsweep response spectrum by applying said attenuation compensation factorto a first magnitude of said first spectral peak, and (v) determine aseverity of an impedance mismatch in said system under test from saidadjusted sweep response spectrum.
 17. The reflectometer of claim 16,wherein:said DSP circuit is further configured to multiply said firstmagnitude of said first spectral peak by said first attenuationcompensation factor.
 18. The reflectometer of claim 16, wherein:said DSPcircuit is further configured to determine that said first magnitude ofsaid first spectral peak is greater than a noise floor level.
 19. Thereflectometer of claim 16, wherein:said DSP circuit is furtherconfigured to (i) obtain a second attenuation compensation factor for asecond distance traveled through said system under test, and (ii)determine said first attenuation compensation factor by interpolatingfrom said second attenuation compensation factor.
 20. The reflectometerof claim 16, further comprising an attenuation compensation table thatincludes a second attenuation compensation factor for a second distancetraveled through said system under test, wherein:said DSP circuit isfurther configured to (i) obtain said second attenuation compensationfactor from said attenuation compensation table, and (ii) determine saidfirst attenuation compensation factor by interpolating from said secondattenuation compensation factor.
 21. The reflectometer of claim 16,wherein:said DSP circuit is further configured to (i) calculate a secondattenuation compensation factor for a second distanced traveled in saidsystem under test, and (ii) determine said first attenuationcompensation factor by interpolating from said second attenuationcompensation factor.
 22. The reflectometer of claim 16, wherein:said DSPcircuit is further configured to calculate said first attenuationcompensation factor by averaging a plurality of attenuation factors forsaid system under test, each attenuation factor of said plurality ofattenuation factors corresponding to said first distance and a differentfrequency.
 23. The reflectometer of claim 16, wherein:said transmitteris further configured to sweep said test sweep signal across a frequencyspan; and said DSP circuit is further configured to calculate said firstattenuation compensation factor by averaging a plurality of attenuationfactors across said frequency span, each attenuation factor of saidplurality of attenuation factors corresponding to said first distanceand a different frequency.